Universal joints that transmit torque from one shaft to another by way of rollers rotating on trunnions that are fixed radially to one shaft, while simultaneously rolling inside of grooves carried by the other shaft are old in the art. They are often referred to as Pot-type joints because of the pot-like appearance of the part in which the rollers and trunnions are contained.
Two types are in commercial use. One uses two diametrically opposed trunnions fixed to one shaft and is non-homokinetic in operation at an angle. The other uses three equally spaced radial trunnions fixed to one shaft and is quasi-homokinetic when operating at an angle, i.e. the output rotation is orbital in nature and not pure rotation. Allowance must be made for this characteristic in any practical applications and for some the joint cannot be used.
Four trunnions can be readily accommodated within the circular cross-sectional area occupied by either of the above types of universal joints, thereby increasing torque capacity considerably with no diametral size penalty. This fact has long been recognized, and a sizeable collection of Prior Art exists featuring four trunnion pot-type joints with near-homokinetic torque transmission. The designs are based on the following concept:
The four trunnions and rollers on one shaft and their mating grooves on the other shaft are, in effect, divided into two universal joints of the two-trunnion type noted above. They are circumferentially spaced at right angles to each other and cooperate in such manner as to average the non-homokinetic rotation of each. The resulting rotation of the output shaft is still non-homokinetic, but of smaller magnitude than that of each two-trunnion joint taken separately.
Some illustrative examples follow:
Orain U.S. Pat. No. 3,975,922 uses torsionally resilient means to connect the two-trunnion joints to the output shaft. The resultant output rotation is an average of two non-homokinetic rotations ninety degrees out of phase.
Wildhaber U.S. Pat. No. 2,672,739 also uses resilient means but in compression between the trunnions to act as an "equalizer".
Anderson U.S. Pat. No. 2,672,740 employs equalizing levers to achieve a similar result.
As the art shows, the concept does not lend itself to a simple reliable design. This is probably the reason why no commercial applications are known.
A totally different concept, believed to be new in the art, is the basis of this invention. It does not unduly restrict design freedom in the choice of proven practical structure that is both compact and strong. Operationally, it ensures dynamic balance coupled with true homokinetic transmission of torque.